This invention relates to an ultrasonic piezo film array on a printed circuit board. More particularly, the present invention relates to an ultrasonic piezo film array on a printed circuit board which has reduced crosstalk and noise pickup by having top and bottom ground planes on opposite sides of the printed circuit and by grounding all connections to the pads except the one from which the input is received.
Ultrasound has been used for a variety of applications in the medical field. This technique is preferable to radiation since there are no bad effects from the use of the ultrasound and the equipment is less costly, smaller in size and easier to use than x-ray equipment. Thus, it has been used in soft tissue imaging, in measuring bone density and in locating cavities in the jawbone and other similar locations. In particular, U.S. Pat. No. 6,030,221 shows an apparatus for detecting bone cavitation utilizing an ultrasonic transmitter and multiplexer with an ultrasonic receiver array.
While such a system is very effective, it is important that the array be as small as possible for easy location and also that the connecting lines be as small as possible. The use of coaxial cable, even if of a small gauge, can present problems, especially when it is necessary for the array to be inside the patients"" mouth. Further, it is important to have as large an array of receiving elements as possible in order to obtain the best image. In addition to this, it is important that crosstalk and noise be eliminated as much as possible so that the relatively small signal is as clear as possible.
Accordingly, these objects have been achieved in the present invention by providing a flexible printed circuit board having four layers, with the outer two layers being ground planes and the inner layers carrying printed circuit lines. An array of pads is provided on the end of the board for receiving piezo elements. The lines are connected to a multiplexer which sequentially accesses each line leading to the elements of the array. All other lines are connected to ground at the same time.
Accordingly, a system is provided which avoids crosstalk and noise and yet provides a small flexible board for carrying an array of receiver elements.